Essential oils and other desirable or useful materials found in botanicals including herbs, fruits, flowers, leaves, skins, stems, stalks, roots, seeds, nuts and berries, have historically been extracted using organic solvents, steam distillation, and/or pressing. For example, butane hash oil (BHO) is the essential oil from the cannabis plant extracted using n-Butane as a solvent and a vacuum oven. Each of these extraction methods has undesirable features: for example, incomplete extraction; the necessity of expensive, toxic, caustic, or flammable solvents having significant disposal costs; damage to the extracted constituents from heat; the inability to specifically target desired for constituents for extraction; difficulty in obtaining solvents for home or small business use; and the need for expert personnel and complex apparatus for performing extractions. Additionally use of extraction solvents such as propane, butane, pentane and hexane, or mixtures of alcohols requires processing beyond the extraction process in order to ensure that the extracted materials are safe for use or consumption.
More recently, supercritical liquids have been used for extracting botanicals, largely alleviating problems associated with heating, the need for expensive, toxic, caustic or flammable solvents having significant disposal costs, solvent availability, and the need for expert personnel. Extractions using subcritical/supercritical carbon dioxide have the advantage that CO2 is non-toxic; non-flammable; operates around room temperature; inexpensive; and environmentally friendly. Further, the extraction efficiency of carbon dioxide for certain compounds may be adjusted by increasing or decreasing pressures and/or temperatures of the carbon dioxide, thereby permitting extractions having varying levels of certain compounds. For example, concentrations of less-desirable plant constituents, such as chlorophyll, can be reduced without secondary processing, by choosing conditions which reduce their solubility in subcritical or supercritical carbon dioxide.